The present invention relates to an optical member inspection apparatus for detecting an optical defect, such as an abnormality in shape or the like, in an optical member such as a lens or the like which may be made by a plastic injection process.
An optical member such as a lens or a prism, etc., is generally designed such that light incident thereupon is refracted regularly, advanced in parallel, converged onto a point or line, or diverged. However, if the optical member contains therein a foreign substance such as a cotton waste or the like (so-called "fuzz"), due to a defective formation thereof, or if the optical member is scratched during handling thereof by an operator, or it foreign matter is affixed to the surface of the optical element, the light incident upon the optical member can be disturbed, thus resulting in a failure to obtain a desired optical property.
Previously, sensory tests relying upon an operator's eyesight have been carried out using a fluorescent lamp or a light source for a slide projector.
In an inspection using a fluorescent lamp or a light source for a slide projector, an optical member is illuminated with light emitted from the lamp or the light source, and the surface of the optical member is observed by an operator outside of the optical path so as to find a detective portion on the surface of the optical member by checking the level of luminance brightness, taking into consideration light reflection, transmission, refraction or the like.
However, such a sensory inspection relying on an operator's eyesight is subjective, there being no definite objective criterion to discriminate a defective product from a non-defective product. Consequently, in the case that the inspection is executed by more than one inspector, the judgment (inspection result) may vary depending upon the inspector. Namely, the same product may be judged "defective" by one inspector and "non-detective" by another inspector. Consequently, a `non-defective` product may unnecessarily be wasted or destroyed. Also, if a defective product is included in a batch of non-defective products, the overall quality of the whole batch is reduced. Moreover, even where the same inspector checks the products, the criterion applied by that inspector tends to become more strict through experience and practice, so that the probability that a non-defective product is mistakenly judged to be a defective product can increase.
Finally, the aforesaid test relies on human operation and is accordingly relatively slow.